Method and device including transistor component having a field electrode

ABSTRACT

A transistor component and method of forming a transistor component. One embodiment provides a semiconductor arrangement including a semiconductor body having a at least one first trench, a first field electrode arranged in the lower trench section of the at least one first trench and being insulated from the semiconductor body by a field electrode dielectric. A dielectric layer is formed on the first field electrode in the at least one first trench, including depositing a dielectric material on a first side of the semiconductor body and on the field plate at a higher deposition rate than on sidewalls of the at least one first trench.

TECHNICAL FIELD

The present disclosure relates to a transistor component having a fieldelectrode below a gate electrode, and to a method of producing suchtransistor component.

BACKGROUND

In transistors having a field electrode below a gate electrode andadjacent to a drift zone the field electrode has different functions: itreduces the a gate-drain capacitance of the component; it shields thegate electrode against high electric field strengths, if the componentis in its blocking state; and it compensates charge carriers in thedrift zone, if the component is in its blocking state, therebyincreasing a maximum blocking voltage of the component.

The field electrode and the gate electrode are insulated from oneanother by a dielectric layer, with the gate electrode, the fieldelectrode and this dielectric layer forming a capacitor. For a givendielectric constant of the dielectric layer between the gate and thefield electrode a capacitance of this capacitor decreases withincreasing thickness of the dielectric layer.

For these and other reasons, there is a need for the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present invention and are incorporated in andconstitute a part of this specification. The drawings illustrate theembodiments of the present invention and together with the descriptionserve to explain the principles of the invention. Other embodiments ofthe present invention and many of the intended advantages of the presentinvention will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

Examples will now be explained with reference to the accompanyingdrawings and the description below. The drawings are intended to explainthe basic principle. Thus, only those features relevant for illustratingthe basic principle are illustrated. Unless stated otherwise, samereference characters designate the same features with the same meaningthroughout the drawings.

FIGS. 1A-1F, illustrate one embodiment of a method of producing atransistor component having a field electrode and a gate electrode and adeposited inter-electrode dielectric arranged between the gate electrodeand the field electrode.

FIGS. 2A-2B, by way of a horizontal (FIG. 2A) and a vertical (FIG. 2B)cross section through the transistor component, illustrate oneembodiment of a way of contacting the gate electrode and the fieldelectrode.

FIGS. 3A-3D, illustrate one example embodiment of a method of producingan inter-electrode dielectric.

FIG. 4 illustrates one embodiment of a transistor cell of the transistorcomponent as produced by the method illustrated in FIG. 1 andillustrates circuit symbols of inherent components of the transistorcell.

FIGS. 5A, 5B illustrate one embodiment of an application including atransistor component as a Low-Side switch and a simplified equivalentcircuit for the commutation of the Low-Side switch.

FIGS. 6A-6J, illustrate one embodiment of a method of producing an edgetermination of a transistor component using the method processes asillustrated in FIG. 1.

FIGS. 7A-7E, illustrate one example embodiment of a method of producinga semiconductor arrangement as illustrated in FIG. 1A.

FIGS. 8A-8F illustrate one example embodiment of a method of producing aMOS gated diode component.

FIG. 9 illustrates one embodiment of a vertical cross section through atransistor component including at least one transistor cell and at leastone MOS gated diode structure.

FIG. 10 schematically illustrates one embodiment of a semiconductorcomponent having several contact trenches with contact electrodes forcontacting the gate and the field electrodes in a transistor arrangementhaving stripe-shaped transistor cells.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which isillustrated by way of illustration specific embodiments in which theinvention may be practiced. In this regard, directional terminology,such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc.,is used with reference to the orientation of the Figure(s) beingdescribed. Because components of embodiments of the present inventioncan be positioned in a number of different orientations, the directionalterminology is used for purposes of illustration and is in no waylimiting. It is to be understood that other embodiments may be utilizedand structural or logical changes may be made without departing from thescope of the present invention. The following detailed description,therefore, is not to be taken in a limiting sense, and the scope of thepresent invention is defined by the appended claims.

One or more embodiments of a transistor device and method, provide foradjusting a thickness of the dielectric layer between the gate and thefield electrodes independently of other dielectric layers, such as agate dielectric layer, in the component. In one embodiment, the methodand device includes a thick dielectric layer between the gate and thefield electrodes.

One embodiment provides a method of forming a transistor component andforming a device having a transistor component. The method includesproviding a semiconductor arrangement having a semiconductor body havinga first side and at least one first trench extending from the first sideinto the semiconductor body. The at least one first trench has sidewallsand lower and upper trench sections. A first field electrode is arrangedin the lower trench section of the at least one first trench andinsulated from the semiconductor body by a field electrode dielectric.The method further includes forming a dielectric layer on the firstfield electrode in the at least one first trench, forming the dielectriclayer including a deposition process that deposits a dielectric materialon the first side of the semiconductor body and on the field plate at ahigher deposition rate than on sidewalls of the at least one firsttrench. A gate dielectric is formed, the gate dielectric at least liningthe sidewalls in the upper trench section of the at least one firsttrench; forming a gate electrode in the upper trench section, the gateelectrode being insulated from the first field electrode by thedielectric layer.

Another embodiment provides a transistor component and device includinga transistor component, including a semiconductor body having a firstside and at least one first trench extending from the first side. The atleast one first trench includes sidewalls and lower and upper trenchsections. A first field electrode is arranged in the lower trenchsection of the at least one first trench and is insulated from thesemiconductor body by a field electrode dielectric. A dielectric layeris positioned on the first field electrode in the at least one firsttrench. A gate dielectric is provided, the gate dielectric at leastlining the sidewalls in the upper trench section of the at least onefirst trench. A gate electrode is in the upper trench section, the gateelectrode being insulated from the first field electrode by thedielectric layer, a thickness of the dielectric layer being at leasthalf of the vertical length of the field plate.

FIGS. 1A trough 1F schematically illustrate one embodiment of a processfor forming a transistor component having a field electrode and a gateelectrode. These figures illustrate the component at various stages ofan exemplary process sequence for forming the component.

Referring to FIG. 1A the process sequence starts with providing asemiconductor arrangement that includes a semiconductor body 100 havinga first side 101, that will be referred to as front side in thefollowing. FIGS. 1A through 1J show a vertical cross section through thesemiconductor body 100, that is a cross section in a plane that runsperpendicular to the front side 101.

Semiconductor body 100 includes at least one first trench 103 thatstarting from the front side 101 extends into the semiconductor body100. In the present example the at least one trench 103 extends in thevertical direction into the semiconductor body 100. In the example theat least one first trench 103 has a rectangular cross section in thevertical plane. However, this is only an example, the at least one firsttrench 103 could have any other trench cross section. According to oneembodiment sidewalls of the trench are tapered (not illustrated) so thatthe at least one first trench 103 narrows with increasing depths.Further edges between sidewalls and a bottom of the at least one firsttrench could be rounded.

The at least one first trench 103 has a lower trench section 103A and anupper trench section 103B. A first field electrode 11 is arranged in thelower trench section 103A and is dielectrically insulated from thesemiconductor body 100 by a first field plate dielectric 21 in thislower trench section 103A. For this purpose first field plate dielectric21 is arranged between the first field electrode 11 and the bottom andthe sidewalls of the trench 103 in the lower trench section 103A.

First field electrode 11 is, for example, made of a metal or a dopedpolycrystalline semiconductor material, such as polysilicon. First fieldelectrode dielectric 21 is, for example, made of an semiconductor oxide,such as silicon oxide. An example embodiment of a method for producingfirst field electrode 11 and first field electrode dielectric 21 will beexplained with reference to FIG. 7.

The at least one first trench 103 is deep, in one embodiment betweenabout 0.75 μm and about 7.5 μm from the first side 101 to its bottomdepending on the breakdown voltage class, i.e. the desired voltageblocking capability, of the MOSFET.

In one embodiment, width of the trench is between about 0.25 μm andabout 2.5 μm. A thickness of the first field electrode dielectric 21 is,for example, between about 75 nm and about 750 nm. The field electrode11 has a vertical length between about 25% up to almost 100% of thedepth of the trench 103. In a transistor component having a voltageblocking capability of, for example, 150 V trench 103 has a depth ofbetween 6 μm and 7 μm, and a body zone (that will be explained furtherbelow) has a vertical dimension of between about 0.5 μm and 1 μm. Thevertical dimensions of the field electrode correspond to about thedeepness of the trench minus the vertical dimension of the body zone.

The distance between two trenches 103 in a direction perpendicular to alongitudinal direction of the trenches 103 is between about 0.3 μm and 3μm, this distance corresponding to a dimension of the semiconductor body100 mesa region between he two trenches.

The lower section 103A of the at least one first trench 103 is thesection that includes the first field electrode 11, the upper section103B is the section between first field electrode 11 and the first side101.

In an optional method process that is illustrated in FIG. 1B adielectric layer 22 is formed on sections of the first field electrode11 that are not covered by the first field electrode dielectric 21. Thisdielectric layer 22 is relatively thin as compared to the fieldelectrode dielectric 21 and is also formed on sidewalls of the firsttrench 103 in the upper trench section 103B and on the front side 101.Forming this dielectric layer 22 is optional, i.e. the method processesthat will now be illustrated with reference to FIG. 1C may be performedwithout first producing the thin dielectric layer 22.

Referring to FIG. 1C a dielectric layer 31 is formed on the first fieldelectrode 11 in the at least one first trench 103. This dielectric layerin the component to be produced will be arranged between the first fieldelectrode 11 and a gate electrode, and will, therefore, be referred toas inter-electrode dielectric in the following. Forming inter-electrodedielectric layer 31 involves a deposition process that deposits adielectric material on the first side of the semiconductor body 101 andon the field plate 11, the deposition process having a higher depositionrate on the front side 101 and on the bottom of the upper trench section103B—where the first field electrode 11 is located—than on sidewalls ofthe upper trench section 103B. Forming inter-electrode dielectric layer31 further involves at least partly removing the deposited dielectricmaterial from the first side 101 and the sidewalls of the upper trenchsection 103B. In the example as illustrated in FIG. 1C the dielectricmaterial has completely been removed from the first side 101 and thesidewalls of the upper trench section 103B, while remaining on or abovethe first field electrode 11. The dielectric material remaining on thefirst field electrode 11 forms the inter-electrode dielectric 31.

Forming the inter-electrode dielectric 31 partly fills the upper trenchsection. Referring to FIG. 1D a gate dielectric 41 is formed onsidewalls of the upper trench section that remains after forminginter-electrode dielectric 31. Gate dielectric 41 is, for example,formed by a thermal oxidation process.

Referring to FIG. 1E the upper section of the at least one trench 103that remains after forming inter-electrode dielectric 31 and the gatedielectric 41 is filled with an electrode material, thereby forming agate electrode 51. The electrode material is, for example, a metal or adoped polycrystalline semiconductor material, such as polysilicon.

Referring to FIG. 1F the component is completed by forming a body zone61 in the semiconductor body 100 adjacent to gate dielectric 41, asource zone 62 in the body zone 61 and adjacent to the gate dielectric41, and a source electrode 65 contacting source zone 62 and body zone61. Body zone 61 and source zone 62 are, for example, formed byimplanting dopants via the first side 101 into the semiconductor body100 before forming source electrode 65. Source electrode 65 in a contacttrench 67 extends into the body zone 61 and in this contact trenchcontacts source zone 62 and body zone 61. However, this is only anexample, any other suitable means for contacting body zone 61 and sourcezone 62 by source electrode 65 may be applied as well. Source electrode65 is electrically insulated from gate electrode 61 by an insulationlayer 66.

The transistor component illustrated in FIG. 1F is a trench field-effecttransistor or trench MOS transistor in which gate electrode 51 isarranged in a trench. Methods for forming a body zone, like body zone61, a source zone, like source zone 62, and a source electrode, likesource electrode 65, of a trench MOSFET are commonly known, so that nofurther explanations are required.

Referring to FIG. 1F the component further includes a drift zone 63 anda drain zone 64, drain zone 64 being contacted by a drain electrode 68.Drain electrode 68 is, for example, comprised of a metal. Drift zone 63is arranged between the drain zone 64 and body zone 61 and is separatedfrom source zone 62 by body zone 61. In the example illustrated in FIG.1F drain zone 64 adjoins a second side 102 of the semiconductor body100. The second side lies opposite to the first side 101 and will bereferred to as a back side of the semiconductor body 100 in thefollowing. Forming drain zone 64 adjacent to the back side 102 is onlyan example. Drain zone 64 may also be realized as a buried layer (notillustrated) that is contacted via a diffused region from the front side101 of the semiconductor body.

Semiconductor body 100 may include two differently doped semiconductorlayers: a higher doped first layer that forms drain zone 64; and a lowerdoped second layer in which the at least one first trench 103 with thefield electrode 11 and gate electrode 51, body zone 61 and source zone62 are formed. Regions having the background doping of the second layerform the drift zone 63 of the component in this example. The first layeris, for example, a semiconductor substrate. The second layer is, forexample, an epitaxial layer formed on the substrate. Instead of using asemiconductor body that has two differently doped layers, a uniformlydoped semiconductor substrate can be used as well, with a backgrounddoping of the semiconductor substrate corresponding to the doping of thedrift zone 63. In this case drain zone 64 is formed by implantingdopants into the back side 102 of the semiconductor substrate.

In one or more embodiments, the component can be a MOSFET or an IGBT.The conductivity type of the device is governed by the doping type ofsource region 62. In an n-type (n-channel) device source region 62 isn-doped, while body zone 61 is p-doped. Drift region 63 has the sameconductivity (doping) type as source zone 62. In a MOSFET drain zone 64is of the same conductivity type as source zone 62, and in an IGBT drainzone 64 is doped complementarily to source zone 62. In a p-channeldevice the doping types of corresponding device zones are complementaryto the doping types in an n-type device. In an IGBT a field-stop zone(not illustrated) of the same conductivity type as drift zone 63, butmore highly doped, may be arranged between drain zone 64 and drift zone63 or in the drift zone 63 distant to drain zone 64.

The transistor component has three terminals: a gate terminal G thatcontacts gate electrode 51; a source terminal S that contacts sourceelectrode 64; and a drain terminal D that contacts drain zone 64. Theseterminals are only schematically illustrated in FIG. 1F.

The component as illustrated in FIG. 1F may include a number ofidentical transistor structures that are commonly referred to astransistor cells. Each transistor cell includes a source zone 62, a gateelectrode 51, and a body zone 61, where two or more cells may share agate electrode 51 and a body zone 61. In the example as illustrated inFIG. 1F the transistor cells share drift zone 63 and drain zone 64. Thetransistor cells are connected in parallel as the gate electrodes 51 arecommonly connected to gate terminal G, and as the source zones 62 arecommonly connected to source terminal S. Transistor cells may have astripe-geometry. In this case, gate electrodes 51 of the individualcells run parallel to each other in a horizontal direction of thesemiconductor body 100.

FIG. 2A illustrates a cross section in a horizontal plane A-A throughone embodiment of an integrated circuit including a semiconductor body100 in which stripe-shaped transistor cells are integrated. FIG. 2Aillustrates the cross section in a region close to the front side 101.FIG. 2B illustrates a cross section in a vertical section plane B-B thatis illustrated in FIG. 2A. Vertical section plane B-B cuts through thefield and gate electrodes 11, 51 in their longitudinal directions.

As can be seen from FIG. 2A, the gate electrodes 51 and the source zone62 of several transistor cells run parallel to each other in thehorizontal plane. Similar to the gate electrodes 51 the first fieldelectrodes 11 of the transistor cells also run parallel to each other.The first field electrodes 11 that, seen from the front side 101, arearranged below the gate electrodes 51 are schematically illustrated inFIG. 2A by dashed lines.

For contacting gate electrodes 51 in common, the device may include afirst contact trench 111 that runs perpendicular to the first trenches103 in the horizontal direction and adjoins the first trenches 103. Thisadditional trench 111 includes a first contact electrode 51′ thatcontacts the gate electrodes 51 arranged in the first trenches 103.These gate electrodes 51 can be contacted by contacting the firstcontact electrode 51′ in the further trench 111. As can be seen fromFIG. 2B the field electrodes 11 are electrically insulated from thefirst contact electrode 51′.

For contacting the field electrodes 11 the device may include a secondcontact trench 112 that includes a second contact electrode 11′. Thefirst and the second contact trench 111, 112 are arranged distant to oneanother in a longitudinal direction of the trenches 103 and, forexample, run perpendicular to these trenches 103. The second contactelectrode 11′ contacts the field electrode but is insulated from thegate electrodes 51 by a further dielectric layer 42. Second contactelectrode 11′ extends to the front side 101 of the semiconductor body,so that the first field electrodes 11 can be contacted from the firstside 101 via contact electrode 11′.

The component may include a plurality of first and second contactelectrodes 51′, 11′ that contact the gate electrode 51 and the fieldelectrodes 11, respectively, in a way illustrated in FIGS. 2A and 2B.Referring to FIG. 2B (see the dash-dotted lines) the trenches thatinclude the gate and the field electrodes 51, 11 may extend beyond thetwo contact trenches 111, 112 that are illustrated in FIG. 2A. In anarrangement having a plurality of first and second contact electrodes51′, 11′ the first and the second contact electrodes 51′, 11′ may bearranged alternately, distant to one another in a longitudinal directionof the trenches, and perpendicular to the trenches that include the gateand the field electrodes 51, 11.

FIGS. 3A through 3D illustrate a first example embodiment of a processsequence for forming inter-electrode dielectric 31 that has beenexplained with reference to FIG. 1D. Referring to FIG. 3A forminginter-electrode dielectric 31 involves depositing a dielectric layer 30on the first field electrode 11 in the at least one first trench 103 aswell as on the first side 101 of the semiconductor body 100. Adeposition process used for depositing dielectric layer 30 is aselective deposition process having a deposition rate that is dependenton an orientation of surfaces on which the dielectric layer 30 is to bedeposited. As illustrated in FIG. 3A the deposition process has a higherdeposition rate on horizontal surfaces than on vertical surfaces. In thepresent case horizontal surfaces are the first side 101 and the bottomof the upper trench section 103B. This bottom of the upper trenchsection 103B is partly formed by the first field electrode 11 and/oroptional dielectric layer 22 (see FIG. 1B). Resulting from the differentdeposition rates dielectric layer 30 has a higher thickness at thebottom of upper trench section 103B and on the first side 101 than onsidewalls of the upper trench section 103B. In one embodiment, thedeposition process is, for example, a high density plasma (HDP) process.The thickness of the dielectric layer 30 that is deposited on horizontalsurfaces, like on the first field electrode 11, is, for example, between200 nm and 300 nm. HDP processes are plasma supported deposition/sputterprocesses that are commonly known, so that no further explanations arerequired.

Referring to FIG. 3B a protection layer 200, such as a resist layer, isformed on the deposited dielectric layer 30. Protection layer 200completely covers dielectric layer 30 and completely fills those partsof the upper trench section 103B that remain after forming thedielectric layer 30. Protection layer 200 is, for example a resist, acarbon, or a carbon-containing layer that can be removed selectivelyrelative to the deposited dielectric layer.

Referring to FIG. 3C protection layer 200 is completely removed fromthose sections of the dielectric layer 30 covering the front side 101,and these sections of dielectric layer 30 covering the front side 101are at least partly removed from the front side 101. “At least partlyremoving” in this connection means that a thickness of dielectric layer30 is at least reduced, if not completely removed. The process ofremoving the protection layer 200 and partly removing the dielectriclayer 30 above the front side, i.e. above the mesa region, stops beforethe protective layer 200 is completely removed from the at least onefirst trench 103, so that a plug 201 of protective material remains inthe trench 103. This plug 201 protects those parts of the dielectriclayer 30 that cover the first field electrode 11 and that form theinter-electrode dielectric 31. In the example as illustrated in FIG. 2Cparts 32 of dielectric layer 30 remain on the first side 101 and plug201 completely fills the upper trench section 103B. However, this isonly an example, the process of removing the protection layer 200 anddielectric layer 30 could also proceed until the dielectric layer iscompletely removed from the first side 101 and until plug 201 onlypartly fills the upper trench section, but still covers first fieldelectrode 11.

The process of partly removing protection layer 200 and dielectric layer30 may involve an etch process that etches both, the material of theprotection layer 200 and the material of the dielectric layer 30. Theetch selectivity for etching the protection layer 200 and the dielectriclayer 30 is, for example, 1:1. This means, that protection layer 200 anddielectric layer 30 are substantially equally etched. However, this etchselectivity may vary in a range of, for example, 0.5:1 to 1:0.5. Theetching process is, for example, a dry etching process that may includean oxygen plasma and chlorine.

Referring to FIG. 3D plug 201 of protection material is removed from theupper trench section 103B. Removing plug 201 may involve a thermalprocess that ashes plug 201 but leaves the remaining parts of dielectriclayer 30, such as inter-electrode dielectric 31.

In an ideal case the deposition rate on the sidewalls of the uppertrench section 103B is zero when depositing dielectric layer 30. In thiscase the semiconductor body 100 is not covered by a dielectric layer atthe sidewalls of the least one first trench after plug 201 has beenremoved. However, in a non-ideal case some dielectric material isdeposited on the sidewalls. Typically a thickness of the dielectriclayer deposited on the sidewalls is between 5 nm and 200 nm. In order toproduce inter-electrode dielectric 31 completely independent of gatedielectric 41 the dielectric materials covering the sidewalls after plug201 has been removed is removed before forming the gate dielectric (41in FIG. 1D).

Removing the dielectric material from the sidewalls may involve anisotropic etch process that also etches parts of the dielectric layer 30that have remained on the front side 101 after the end of the removalprocess that has been illustrated with reference to FIG. 3C. This etchprocess may also etch parts of the inter-electrode dielectric 31.

FIG. 4 schematically illustrates a transistor cell of a transistorcomponent produced in accordance with the method as explained withreference to FIG. 1. FIG. 4 further shows the circuit symbol M of thetransistor component as well as circuit symbols of parasitic resistancesand capacitances of the transistor component. The transistor symbol Millustrated in FIG. 4 relates to an n-channel MOSFET. However, this isonly an example. The circuit diagram as illustrated in FIG. 4 alsoapplies to a p-channel MOSFET in an equivalent manner. As illustrated inFIG. 4 the component has five relevant inherent capacitances: agate-source capacitance C_(GS) that is formed by gate electrode 51, gatedielectric 41, source zone 62, body zone 61 and source electrode 65; agate drain capacitance C_(GD) that is formed by gate electrode 51, gatedielectric 41 and drift zone 63; a drain-source capacitance C_(DS)formed by drift zone 63 and body zone 61; a gate-field-electrodecapacitance C_(GFP) that is formed by gate electrode 51, inter-electrodedielectric 31 and first field electrode 11; and a drain-field-platecapacitance C_(FP), that is formed by first field electrode 11, fieldelectrode dielectric 21, drift zone 63 and drain zone 64. First fieldelectrode 11 is either electrically connected to source terminal S or togate terminal G. for explanation purposes it is assumed that fieldelectrode 11 is electrically connected to source terminal S. In thiscase there is a field-electrode resistance R_(FP) between sourceterminal S and field electrode 11. The component further includes a gateresistance R_(G) that is present between gate terminal G and gateelectrode 51. Both R_(FP) as well as R_(G) are no lumped resistors butrather inherent differential resistances of incremental elements of thestripe-shaped electrodes.

The capacitances and parasitic inductances L_(STRAY) influence theswitching behaviour of the component. In particular in applications inwhich the transistor M is alternately biased in its reverse directionand forward direction high frequent oscillations may occur. FIG. 5illustrates an example of such an application. In this exampletransistor M acts as a low-side switch of a half-bridge circuit. Forthis purpose load path (drain-source-path) of transistor M is connectedin series to a high-side switch HS, the series circuit with the low-sideand the high-side switches is connected between terminals for supplyingan input voltage Vin. A circuit node common to low-side and high-sideswitch forms an output, that is also referred to as phase node PN, ofthe half-bridge circuit. In the present example an inductive load isconnected to the phase node. Inductive load includes at least oneinductance L. In the example as illustrated in FIG. 5 the inductive loadis an output stage of a buck converter that besides inductance Lincludes an output capacitance C for providing an output voltage Vout. Aseries circuit including inductance L and output capacitance C isconnected parallel to low-side switch M.

In this circuit low-side switch M acts as a free-wheeling element thatby control signal S2 is switched on each time high-side switch HS by acontrol signal S1 is turned off. If high-side switch HS is turned on andlow-side switch M is turned off load L, C is connected to the inputvoltage Vin. Subsequently high-side switch HS turns off and low-sidesignal S2 turns on low-side switch M which allows a free-wheelingcurrent to flow driven by the inductive load. In order to avoidshoot-through currents between the supply terminals there is a delaytime (dead time) between switching off low-side switch M and switchingon high-side witch HS and vice versa. During the dead time the internalbody diode BD of the transistor component takes over the freewheelingcurrent. Referring to the cross section illustrated in FIG. 4 the bodydiode between source and drain terminal S, D is formed by thepn-junction between body zone 61, that is contacted by source electrode65, and drift zone 63. In an n-type transistor a forward direction ofthe body diode is from source S to drain D.

In the application illustrated in FIG. 5A the body diode ofLow-Side-Switch M is forward biased when low-side switch M is switchedoff and until high-side switch HS switches on. At a time when high-sideswitch HS switches on the body diode of low-side switch M isreverse-biased. At this time an abrupt voltage change occurs acrossdrain-source-path of low-side switch M. This abrupt voltage changeexcites an oscillator circuit that is formed by the transistorcapacitances and parasitic stray inductances that are present in thehalf-bridge having input supply voltage source Vin, high-side switch HSand low-side switch M. These stray inductances are represented by alumped inductance L_(STRAY) in FIG. 5A. The excited oscillator circuitcauses voltage overshoots at the phase node which may harm the outputstages of the driver for the high-side switch. It can be illustratedthat relevant components for damping such oscillations in the parasiticoscillator circuit are the gate-field-plate capacitance C_(GFP) andfield-plate resistance R_(FP).

In typical applications the frequency of the parasitic oscillations isin a range of between 100 MHz and 200 MHz. At this frequency the (AC)impedance of the gate-source capacitance C_(GS) is significantly smallerthan the gate resistance R_(G). For damping purposes gate resistanceR_(G) may therefore be neglected compared with gate-source capacitanceC_(GS). Further, the gate-field-plate capacitance C_(GFP) is usuallysmaller than the gate-source capacitance C_(GS), so that in the seriescircuit including these two capacitances C_(GS), C_(GFP) thegate-field-plate capacitance C_(GFP) is dominant. Further, drain-sourcecapacitance C_(DS) may be neglected compared with drain-field-platecapacitance C_(DFP), and gate-drain capacitance C_(GD) may be neglected.

The parasitic oscillator circuit that is excited when switching low-sideswitch M can therefore be reduced to a circuit illustrated in FIG. 5B.Such circuit includes the stray inductance L_(STRAY), thedrain-field-plate capacitance C_(DFP), the gate-field-plate capacitanceC_(GFP), and the field-plate resistance R_(FP), with the strayinductance L_(STRAY) and the drain-field-plate capacitance C_(DFP) beingconnected in series, and with a parallel circuit including thegate-field-plate capacitance C_(GFP), and the field-plate resistanceR_(FP) being connected in series with the series circuit including thestray inductance L_(STRAY) and the drain-field-plate capacitanceC_(DFP).

Oscillations of the parasitic oscillator can be damped, and voltageovershoots can therefore be reduced, by increasing a resistance value offield-plate resistance R_(FP) and/or by reducing a capacitance value ofgate-field-plate capacitance C_(GFP). The capacitance value ofgate-field-plate capacitance C_(GFP) decreases with an increasingthickness of the inter-electrode dielectric 31.

A thickness of the inter-electrode dielectric 31 is at least half (50%)of a vertical length of the field electrode 11. Since the thickness ofthe inter-electrode dielectric 31 and a vertical length of the fieldelectrode 11 may vary in a lateral direction of the trench, thisrelationship is at least valid in the middle of the trench, the middleof the trench being the middle between two mesa regions that adjoin thetrench 103 on opposite sides. According to an example the thickness ofthe inter-electrode dielectric 31 is less than, or equal to, thevertical length of the field electrode 11. In this case a relationshipbetween the thickness d₃₁ of the inter-electrode dielectric 31 and thevertical length l₁₁ of the field electrode 11 is between 1:2 and 1:1.

The depth (vertical dimension) of the trench 103 affects the outputcapacitance of the transistor component, with the output capacitanceincreasing with increasing trench depth. To a given trench depth a givenoutput capacitance corresponds. For a given trench depth an arrangementincluding the inter-electrode dielectric 31 and the field electrode 11have a given vertical dimension. For a given output capacitanceincreasing the thickness of the inter-electrode dielectric 31 results ina decreasing vertical length of the field electrode 11. Decreasing thevertical length of the field-electrode, however, decreases its crosssection, and therefore increases its resistance. For a given outputcapacitance increasing the thickness of the inter-electrode dielectrictherefore affects both, the gate-field-plate-capacitance C_(GFP)—that isdecreased—and the field plate resistance—that is increased. Both effectsimprove damping of parasitic oscillations.

For further increasing the field-plate resistance additional measuresmay be taken. These measures may include increasing a line resistance ofa connection line between the source terminal S and the field plate.This may involve adjusting the resistance of the contact electrode 11′that has been illustrated with reference to FIG. 2.

The method as illustrated with reference to FIG. 1 allows to adjust thethickness of inter-electrode dielectric 31 independently of the fieldelectrode dielectric 21 and gate dielectric 41.

When making slight modifications the method as illustrated withreference to FIG. 1 may also be used for producing an edge terminationof a transistor component. An edge termination is a structure thatterminates the transistor cell area. The edge termination may bearranged close to the edge of the semiconductor body. However, the edgetermination can also be arranged distant to the edge, in particular ifbesides the transistor component other components, like logic circuits,are integrated in the semiconductor body.

An example of a method for producing edge terminations using the methodsas illustrated with reference to FIG. 1 will no be illustrated withreference to FIGS. 6A through 6J. Referring to FIG. 6A semiconductorbody 100 includes a second trench 105 in an edge region 104, the secondtrench 105 extending into the semiconductor body 100 starting from firstside 101. For a better understanding first trenches 103 each including afirst field electrode 11 are also illustrated in FIGS. 6A through 6J.The first trenches 103 illustrated in these figures are two of aplurality of first trenches 103. The region in which the first trenchesare disposed will be referred to as cell region in the following.

Second trench 105 includes a second field electrode 12 that is insulatedfrom the semiconductor body 100 by a second field electrode dielectric23. The second field electrode dielectric 23 concerning its material andthickness may correspond to the first field electrode dielectric 21. Thesecond field electrode 12 in a vertical direction extends to the firstside 101 or beyond the first side 101 of the semiconductor body 100. Thesecond field plate dielectric 23 covers the front side 101 in the edgeregion 104 and the side wall of trench 103′ that lies in the directionof the second trench 105.

Referring to FIG. 6B in the optional method process of producing a thindielectric layer 22 on the first field electrode 11 a thin dielectriclayer 22 is also produced on the second field electrode 12.

Referring to FIG. 6C dielectric layer 30 that is deposited on the firstfield electrode 11 in the first trench 103 in the edge region 104 isdeposited on the second field electrode dielectric 23 and on the secondfield electrode 12.

Referring to FIG. 6D protection layer 200 that fills the upper trenchsection of the first trenches 103 completely covers dielectric layer 30in the edge region 104. Protection layer 200 is thicker above thedielectric layer 30 in the edge region 104 than above the dielectriclayer 30 in the cell region because a significant amount of theprotection layer that is applied on the cell region flows into the firsttrenches 103 and completely fills these trenches 103.

After the method process that removes protection layer 200 above thefront side 101 and that at least partly removes dielectric layer 30above the first side 101 a part 32′ of dielectric layer 30 remains abovethe first side 101 in the edge region 104. The part 32′ of thedielectric layer 30 that remains in the edge region is thicker than thepart 32 remaining in the cell region. That reason is that the protectionlayer has different thicknesses in the edge region and in the cellregion. When removing the protection layer 200 dielectric layer 30 iscompletely uncovered in the cell region earlier than in the edge region,so that during this process more from the dielectric layer is removed inthe cell region than in the edge region 104. Protection layer 200 iscompletely removed both, in the cell and in the edge region.

The etch termination structure that includes the second field electrode12 and the second field dielectric 30 and that is covered by a part ofdielectric layer 30 is not affected by the subsequent method processesof forming a gate dielectric and a gate electrode in the first trench103. These method processes that are illustrated in FIGS. 6F to 6I andthat have already been explained with reference to FIGS. 3D and 1C to 1Einclude removing the protection layer plug 201 from the first trench 103(see FIG. 6F), removing the dielectric layer 103 from the side walls ofthe upper trench sections of the first trench 103 (see FIG. 6G), formingthe gate dielectric 41 (see FIG. 6H) and forming gate electrode 51 (seeFIG. 6I).

The process sequence that has been illustrated with reference to FIGS.1A through 1E starts with the semiconductor arrangement that includes afirst field electrode 11 in at least one first trench 103. An example ofa method for producing such semiconductor arrangement will now beexplained with reference to FIGS. 7A through 7E. Referring to FIG. 7A ina first method process first trenches 103 are produced in asemiconductor body 100. Forming the trenches may involve any knownmethod for forming trenches in a semiconductor body, such as etchingprocesses.

Referring to FIG. 7B a field electrode dielectric layer 20 is formed onthe first side 101, on sidewalls and at the bottom of the first trenches103. This field electrode layer 20 in a later stage forms the firstfield electrode dielectric (21 in FIGS. 1B through 1E). Forming thefield electrode dielectric layer 20 may involve a thermal oxidationand/or a deposition process.

Referring to FIG. 7C an electrode layer 10 that, at a later stage, formsthe first field electrode 11 is deposited so as to completely fill thefirst trenches 103.

Referring to FIG. 7D electrode layer 10 is etched back in the firsttrenches 103 so as to form the first field electrodes 11 in the bottomsection 103A of the first trenches 103. Etching back the electrode layer11 may involve an anisotropic etch process.

Referring to FIG. 7E field electrode dielectric layer 20 is removed fromthe first side 101 and the sidewalls of the upper trench sections 103B.This may involve an isotropic etch process. The process as illustratedwith reference to FIGS. 7A through 7E is also suitable for forming asecond field electrode 12 as illustrated in FIGS. 6A through 6I. Forforming the second field electrode 12 electrode layer 10 (see FIG. 7C)is first removed down to the field electrode dielectric layer 20. Thenthe trench in which the second field electrode 12 is to be produced iscovered by a protection layer and stays covered until the end of theprocess processes illustrated in FIGS. 7D and 7E.

According to a further embodiment of a method of producing a transistorcomponent a gated diode structure, also commonly known as MOS gatesdiode structure or MOS diode structure, is formed in at least one thirdtrench 106 of the semiconductor body 100 before the method processesthat have been illustrated with reference to FIGS. 1A through 1E areperformed. An example of a process sequence for forming such gated diodestructure will now be illustrated with reference to FIGS. 8A through 8F.These figures schematically illustrate a vertical cross section throughthe semiconductor body 100 at various stages of the process sequence.

Referring to FIG. 8A the process sequence for forming the gated diodestructure starts with the semiconductor arrangement that has beenillustrated with reference to FIG. 7C and that includes trenches thathave their side walls and bottom covered with the field electrodedielectric layer 20 and that are filled with the electrode material 10.Electrode layer 10 is, for example, deposited so as to completely coverfield electrode dielectric layer 20.

Referring to FIG. 8B electrode layer 10 is then removed down to thefield electrode dielectric layer 20 above the first side 101 but staysin the trenches. Reference symbol 10′ designates plugs of the electrodematerial that remain after removing electrode layer 10 above the firstside 101.

Referring to FIG. 6C the plug 10′ in at least one of the trenches isthen covered by a protection layer 301. The trench in which theprotected plug 113′ is arranged will be referred to as third trench 106in the following. The contact plug in this third trench forms a thirdfield electrode 13, which is a field electrode of the gated diodestructure. For illustration purposes trenches that have their electrodeplugs not covered by a protection layer are also illustrated in FIGS. 8Athrough 8F. These trenches are first trenches 103 in which first fieldelectrodes 11 and gate electrodes will be formed.

Referring to FIG. 8C protection layer 301 protects the third fieldelectrode 13 from being etched when etching electrode plugs 10′ in thefirst trenches 103 to form the first field electrodes 11.

Referring to FIG. 8D protection layer 301 is removed and field electrodedielectric layer 20 is removed from the first side 101, and fromsidewalls of the upper trench sections of first and third trenches 103,106. Removing the field electrode dielectric layer 20 from the sidewallsof the upper trench sections involves, for example, an isotropic etchprocess. After removing dielectric layer 20 from the side walls of theupper trench sections dielectric layer 20 still covers the bottom andthe side walls of the lower trench sections, thereby forming the firstfield electrode dielectric 21 in the first trenches 103 and a thirdfield electrode dielectric 24 in the third trench 106.

By removing field electrode dielectric layer 20 from sidewalls of theupper trench section in the third trench 106 a space is formed betweenthird field electrode 13 and the sidewalls of the third trench 106 inthe upper trench section. Also referring to FIG. 8D a dielectric layer71 is formed on the third field electrode 13 and on the sidewalls of thethird trench 106 in the upper trench section. Forming this dielectriclayer 71 may include a thermal oxidation process and/or a depositionprocess. In this process the dielectric layer 71 is also formed on thefirst side 101 and on a bottom and on the sidewalls of the at least onefirst trench 103. This dielectric layer may correspond to the optionaldielectric layer 22 that has been explained with reference to FIG. 1B.

The thickness of dielectric layer 71 is selected so that dielectriclayer 71 does not completely fill the space between third fieldelectrode 13 and the semiconductor body 100. Referring to FIG. 8E thisspace is filled by an electrode material. Filling the space may involvedepositing an electrode layer 80 on the semiconductor arrangement.Subsequently, as illustrated in FIG. 8F, electrode layer 80 is removedfrom the first side 101 and from sidewalls and the bottom of the atleast one third trench 103, but remains in the space between the thirdfield electrode 13 and the semiconductor body 100, forming a gateelectrode 81. Those parts of the gate diode structure that are arrangedin the third trench 106 are completed at the end of the method processillustrated in FIG. 8F. Starting with the structure illustrated in FIG.8F the method processes as illustrated with reference to FIG. 1 can nowbe performed in order to complete the transistor structures in the firsttrenches 103.

FIG. 9 illustrates a vertical cross section through a device that isobtained by applying the method processes as illustrated with referenceto FIG. 1 on the semiconductor arrangement illustrated in FIG. 8F. FIG.9 illustrates a section of the component in which the transistor celland a MOS gated diode cell are arranged. MOS gated diode structureincludes gate electrode 81, source zone 62 and body zone 61. Gateelectrode 81 of the MOS gated diode structure may be connected to thesource terminal S of the transistor. The third field plate 71 isconnected to the source terminal of the transistor. By connecting thegate electrode 81 of the diode structure to source terminal the diodeconducts or blocks dependent on a voltage difference between the sourceand the drain terminal. In an n-type transistor the MOS gated diodeconducts each time the voltage at source terminal S rises above thevoltage at the drain terminal D. In this case an n-channel is formed inbody zone 61 along gate dielectric 71 between drift zone 63 and sourcezone 62 due to the very low threshold voltage of the MOS gated diode.

In one embodiment, the function of the MOS gated diode structure issubstantially the same as the function of the body diode. However,forward voltage drop and reverse storage charge of the MOS gated diodeis lower as compared to the conventional body diode.

As it has been discussed with reference to FIGS. 4 and 5 the crosssection of the field electrodes 11 influences the field-plate resistanceR_(FP). Besides the cross section the field plate resistance may beinfluenced or adjusted by suitably selecting the electrical resistanceof an connection line between the source electrode 65 and the fieldelectrodes 11. In an arrangement in which the field electrodes 11 arecontacted by second contact electrodes (see 11′ in FIGS. 2A and 2B) theelectrical resistance of the connection line is dependent on the crosssection of the second contact electrodes 11′ and on the number of secondcontact electrodes 11′. This will be explained with reference to FIG.10.

FIG. 10 schematically illustrates a top view on a semiconductor body 100in which active areas, gate electrodes and field electrodes ofstripe-shaped transistor cells are integrated. In the schematic drawingof FIG. 10 only the trenches 103—in which the gate and the fieldelectrodes are arranged—of the stripe-shaped transistor cells areillustrated. The gate electrodes arranged in the trenches 103 arecontacted by first contact electrodes 51′ that—in the example—runperpendicular to the gate electrodes. Referring to FIGS. 2A and 2B thefirst contact electrodes 51′ may be arranged in trenches. The fieldelectrodes arranged in the trenches are contacted by second contactelectrodes 11′ that—in the example—run perpendicular to the fieldelectrodes. Referring to FIGS. 2A and 2B the second contact electrodes11′ may be arranged in trenches. It should be noted that FIG. 10 servesto illustrate the position of the trenches 103 and the contactelectrodes 51′, 11′, so that the contact electrodes 51′, 11′ are onlyschematically illustrated. Insulation layers that, for example, insulatethe second contact electrode from the gate electrode are notillustrated.

The arrangement according to FIG. 10 includes a gate pad 50 to which thefirst contact electrodes 51′ are electrically coupled. Gate pad 50 isconnected to the gate terminal G (not illustrated in FIG. 10) thatserves for applying a gate potential. The second contact electrodes 11′that contact the field electrodes are contacted by the source electrode65 (not illustrated in FIG. 10). For the arrangement in FIG. 10 thefield plate resistance R_(FP) that has been explained with reference toFIG. 4 is approximately given by

$\begin{matrix}{R_{FP} = {\frac{1}{3}\rho{\frac{p}{A} \cdot \frac{1}{\left( {n + {2m}} \right)^{2}} \cdot \frac{l}{b}}}} & (1)\end{matrix}$where

-   μ is the specific resistance of the material of the field plate;-   p is the cell pitch, which is the distance between the middle of one    trench 103 and the middle of the neighboring trench 103;-   A is the cross section of the field plate 11;-   n is the number of connections to the field plates 11 at the edge of    the cell area;-   m is the number of connections to the field plates 11 in the cell    area;-   l is the length of the transistor cells;-   b is the width of the cell area, which is the dimension in a    direction perpendicular to a longitudinal direction of the    transistor cells.

In the example according to FIG. 10 n=0 and m=3, with m being the numberof the second contact electrodes 11′. It should be noted that using m=3second contact electrodes 11′ is only an example. It goes without sayingthat any number other than 3 may be used as well, where m is, inparticular, greater than 1. Referring to eqn. (1) besides the crosssection A the field plate resistance R_(FP) may be adjusted by varyingthe number of second contact electrodes 11′, the field plate resistanceR_(FP) decreasing with the number of second contact electrodes 11′increasing.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments illustrated and describedwithout departing from the scope of the present invention. Thisapplication is intended to cover any adaptations or variations of thespecific embodiments discussed herein. Therefore, it is intended thatthis invention be limited only by the claims and the equivalentsthereof.

1. A transistor component, including: a semiconductor body having afirst side and at least one first trench extending from the first side,the at least one first trench having sidewalls and lower and uppertrench sections; a first field electrode arranged in the lower trenchsection of the at least one first trench and being insulated from thesemiconductor body by a field electrode dielectric, the first fieldelectrode having a vertical length; a dielectric layer on the firstfield electrode in the at least one first trench; a gate dielectric, thegate dielectric at least lining the sidewalls in the upper trenchsection of the at least one first trench; a gate electrode in the uppertrench section, gate electrode being insulated from the first fieldelectrode by the dielectric layer, a thickness of the dielectric layerbeing at least 50% of the vertical length of the field electrode; anedge region of the semiconductor body; a second trench arranged in theedge region, and extending from the first side into the semiconductorbody; a second field electrode arranged in the second trench, the secondfield electrode being insulated from the semiconductor body by a secondfield electrode dielectric, and extending further in the direction ofthe first side than the first field electrode.
 2. The transistorcomponent of claim 1, wherein the thickness of the dielectric layer isless than or equal to the vertical length of the first field electrode.3. The transistor component of claim 1, wherein the thickness of thedielectric layer is a thickness in the middle of the trench and ismeasured in a vertical direction of the semiconductor body, and whereinthe vertical length of the first field electrode is a length in themiddle of the trench and is measured in a vertical direction of thesemiconductor body.
 4. The transistor component of claim 2, wherein thesecond field electrode extends to the first side or beyond the firstside.
 5. The transistor component of claim 1, further including a MOSgated diode structure, the MOS gated diode structure including: a thirdtrench in the semiconductor having a lower trench section and an uppertrench section; a third field electrode arranged in the third trench andinsulated from the semiconductor body by a third field electrodedielectric in the lower trench section; a second gate electrode arrangedbetween the third field electrode and the semiconductor body in theupper trench section, and insulated from the semiconductor body and thethird field electrode by a dielectric layer.